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Procedia Engineering 120 (2015) 484 – 487
EUROSENSORS 2015
LTCC, New Packaging Approach for Toxic Gas and Particle
Detection
Anita Lloyd Spetza,b,*, Maciej Sobocinskib, Niina Halonenb, Donatella Puglisia, Jari
Juutib, Heli Jantunenb, Mike Anderssona,b
a
Div. Applied Sensor Science, Dept. Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
b
Microelectronics and Material Physics Laboratories, University of Oulu, P.O. Box 4500, FIN-90014,Oulu, Finland
Abstract
Packaging of chemical sensors is still an area, which is not much explored. Low temperature co-fired ceramic, LTCC, packaging
offers large advantages in terms of 3D design, integration of advanced functionality and fast processing. SiC based FET gas sensors
are possible to integrate directly in the LTCC co-firing process at 850°C, whereby both high temperature and other advanced
applications like ultra-low detection of toxic gases are greatly improved. The LTCC packaging is also used for development of
particle detectors as well as packaging for an electrical method to detect toxic effect on cells by particles.
©
Authors.
Published
by Elsevier
Ltd. This
is an open access article under the CC BY-NC-ND license
2015The
The
Authors.
Published
by Elsevier
Ltd.
©2015
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review
under
responsibility
of
the
organizing
committee
of EUROSENSORS
2015.
Peer-review under responsibility of the organizing committee
of EUROSENSORS
2015
Keywords: LTCC technology, SiC-FET gas sensors, particle sensors, cell-clinic
1. Introduction
Low Temperature Co-fired Ceramic, LTCC, is a sophisticated packaging technology developed since the 1980’s
and now used for embedded electrical circuits, buried passive components in applications such as automotive,
telecommunication and hand-held electronics [1]. Continuous material and processing development offers benefits
like parallel processing, hermetic packaging, resistance to harsh environments and high temperatures and cost
* Anita Lloyd Spetz. Tel.: +46 705 176788;
E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
doi:10.1016/j.proeng.2015.08.677
Anita Lloyd Spetz et al. / Procedia Engineering 120 (2015) 484 – 487
485
effectiveness e.g. through fast processing. The technology is based on commercially available green tapes where e.g.
conducting lines, finger electrodes and cavities are processed. Recently a tape, HeraLock 2000 (Heraues GMbH,
Germany), with almost no planar shrinkage during the firing process was discovered [2], whereby also bulk materials
may be integrated within the LTCC package [3]. One of the advantages of the LTCC is the integration of electrical
connections eliminating wire bonding and encapsulation. For the SiC-FET gas sensors the LTCC packaging is suitable
for gas sensing in high temperature and corrosive environment as well as many other applications.
The new generation of SiC-FET gas sensors [4] have been commercialized for control of small and medium sized
bioheaters (www.sensic.se). Several applications have been demonstrated for harsh environment and high temperature
such as an ammonia sensor for control of the selective catalytic reduction, SCR, a process where urea is introduced in
a diesel engine exhaust system for reduction of nitric oxide gases [5]. Recently it has also been shown that the SiCFET devices, for example utilizing a porous Ir gate, are able to detect ultra-low concentrations, in the low parts per
billion (ppb) range, of indoor toxic gases like formaldehyde, benzene and naphthalene [6].
Not only gas molecules but also particles show adverse effects on our health and need to be controlled. Commercial
detectors are e.g. based on charging of the particles and separation of them in an electric field. The LTCC technology
has the potential to provide portable and cheap particle detectors [5].
A so called cell clinic was developed for electrical monitoring of cell activity using a capacitance sensing CMOS
chip [7]. This method is developed for measuring cell activity during particle exposure in order to determine toxic
effect of particles on cell growth. A LTCC housing has been developed for the CMOS chip.
Here we report on the use of the LTCC packaging for SiC-FET gas sensor devices and an example of gas sensing
by these devices. Furthermore, we report about the potential use of LTCC packaging for a particle detector and its use
as a housing for a CMOS chip for capacitive measurements of cell growth to monitor the influence of particle exposure
on cell viability.
2. Experimental
For the LTCC packaging the green tape HeraLock 2000 (Heraues GMbH, Germany) has been used. More details
can be found in a paper by M. Sobocinski et al, this proceeding.
The SiC-FET devices are designed by SenSiC AB and processed by ASCATRON AB, Stockholm, Sweden [4].
More details about the LTCC packaged CMOS chip used for capacitive monitoring of cell growth during particle
exposure is found in a paper by N. Halonen et al, this proceeding.
Fig. 1. (a) SiC FET devices processed on 4” SiC wafer (design SenSiC AB, processing ASCATRON AB, Sweden), (b) close up of the wafer
showing several sensor chips, (c) one sensor chip hermetically integrated in the LTCC packaging, (d) schematic picture of the LTCC package
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Anita Lloyd Spetz et al. / Procedia Engineering 120 (2015) 484 – 487
3. SiC-FET sensors
The SiC-FET device has been integrated in a LTCC package in one processing step, M. Sobocinski et al, this
proceeding. This is possible due to the material properties of silicon carbide and the sturdy design of the transistor
based sensor chips. The IV curves were slightly changed after the processing but the devices were still fully
functioning also as gas sensors. Except for eliminating the tricky bonding step for the SiC-FET devices, the LTCC
packaging also has big advantages like easy integration of functionality in the packaging, see schematic pictures in
Figure 1 and 2.
The silicon carbide based transistors function as gas sensors due to the catalytic gate metal, normally porous, which
is utilized as the sensing layer. Gas molecules adsorb and react on the catalytic metal surface, reaction products charge
the insulator surface exposed in the pores of the catalytic metal. The formed electric field influences the current
through the transistor and this change in current is the sensor response to gas molecules.
The LTCC packaging increases the commercial potential of the SiC-FET technology in many different areas.
Applications are possible at high temperature as well as room temperature. Indoor atmosphere contains volatile
organic compounds, VOC, such as formaldehyde, benzene and naphthalene, which are toxic already at ppb levels [8].
The SiC-FET devices in the laboratory successfully detected these three gases also in an atmosphere of high humidity
with a detection level of 1 ppb for benzene, 0.5 ppb for naphthalene and 10 ppb for formaldehyde.
4. Particle detectors
The LTCC technology is also being developed for detection of particles, since these may be a threat to our health.
Parameters that influences the toxic effect of particles are e.g. the size, shape, concentration and content or adsorbents
on the particles. Particles may be collected and separated by applying a low temperature and/ or an electric field and
also a magnetic field will give information, see Fig. 2. Finger electrodes may be used for resistivity measurements or
impedance spectroscopy and has the potential to detect size and concentration of the particles. Heating the particles
and detection of the emissions has been demonstrated to detect ammonia released from ash particles that originates
from a power plant with an SCR system to reduce nitric oxide gases [9].
Fig. 2. Schematic picture of a particle detector based on LTCC technology. A and B. Particles are collected by a low temperature and separated
by electric fields. C1 and C2. Particles are heated and the emitted gases detected by an integrated gas sensor (or gas sensor array). Finger
electrodes are used for impedance spectroscopy of the particles.
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5. The toxic effect of particles on cells
A CMOS chip has been developed to perform capacitive measurements of the viability of cells [7]. The method is
extended to an electrical method to detect the influence of particles on cells. For this the CMOS chip is packaged
using LTCC technology, see Fig. 3. The green tape used for this is the HeraLock 2000, which is considered not
biocompatible. A special mounting solved this, see N. Halonen et al, this proceeding. Cell growth was normal in the
final device. Many different particles are interesting to test and a mammalian cell culture is used for the experiments,
which are performed in an incubator. The goal is to develop this method to also function outside the incubator, to
make it a compatible method for studying toxic effects on cells by particles.
Fig. 3. CMOS chip (insert) glued to the LTCC package. Cavity for cell growth media and preliminary testing of particles. The LTCC substrate is
connected to zero insertion force (ZIF) connector
6. Conclusion
The LTCC packaging technology is very interesting for both gas and particle detection because of easy 3D
processing and possibility to include several kinds of functionality. We have demonstrated integration of a SiC-FET
gas sensor in a one-step firing process. The LTCC is also developed for particle detection and analysis and as an
electrical method to study the influence of particles on cells.
Acknowledgements
Funding is acknowledged from Finland: TEKES (CHEMPACK #1427/31/2010), Academy of Finland (ClintoxNP
#268944), from Sweden: VINNOVA (VINN Excellence center FunMat) Swedish Research Council (#621-20124497), and support from the COST network EuNetAir TD1105 is also acknowledged.
References
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